Devices for transforming a first rotary motion into a secondary motion (which is generally a further rotary motion, but which may be a rectilinear motion) are known.
When both motions are rotary motions, the device includes two shafts about which the said two rotary motions take place, with the device acting to modify the ratio of the angular speeds of said rotations.
Very often, the two rotary shafts in such a device run along a common axis. The speed reducer can then be mounted directly on the output shaft from a motor, which the motor output shaft constituting the high speed shaft. The slow shaft then lies on the same axis as the motor shaft.
Such prior art devices are generally reversible, that is to say that they can also be used to increase a speed.
Such devices have numerous uses, for example in robotics, in machine tool control, etc., where they are generally used as speed reduction gears.
Of the various types of motion-transforming device of this nature, specific mention may be made, for example, of gear train devices, and in particular of devices of the epicyclic type, or else devices having eccentric drive.
A particular drawback of these known devices lies in the backlash they introduce which makes them difficult to use for precision mechanisms.
Devices are also known comprising an elliptical bearing in which a flexible ring having external teeth is deformed, said ring driving a rigid ring having internal teeth. Such devices introduce a degree of elasticity which reduces performance and may give rise to changes in motion, in particular if there are major changes in torque.
Finally, all of these devices suffer from a common drawback of operating only at a relatively low inlet speed, and of giving rise to friction which reduces overall efficiency as well as requiring the use of a lubricant. Another, additional drawback lies in added inertia about the high speed axis.
Motion transforming devices are known comprising: a first stage with two moving members, at least one of which is operationally coupled to a shaft generating a first motion which is a rotary motion; a second stage comprising at least one set of two pulleys constrained to rotate together and co-operating with transmission means, for example with two endless drive strands which co-operate with the moving members of the first stage; and a moving support which supports the two pulleys of the second stage so that they are free to rotate and whose displacement along an imposed trajectory generates a second motion.
In known devices of this type, the moving support is coupled to the high speed shaft and this suffers from the drawback of generating friction and inertia on said shaft.
One of the aims of the present invention is to provide a motion transforming device which provides advantages over prior art devices.
Another aim of the invention is to provide such a motion transforming device which can be used, in particular, as a speed reduction gear.
Another aim of the invention is to provide such a device suitable for transforming a rotary motion into another rotary motion, or else into a displacement motion along a non-circular curved trajectory which may be planar or otherwise, and vice versa.